Shielding system for vapor-converters.



s. w. FARNSW ORTH. SHIELDING SYSTEM FOR VAPOR CONVERTERS..

APPLiCATlON FILED 36.9. 1915.

Patented July 3, 1917.

INVENTOR WITNESSES @FFIQE SIDNEY W. FARNSWORTH, OF PITTSBUB GHQPENNSYLVANIA,- ASSIGNOR TO WESTING- I HOUSE ELECTRIC AND 'MANUFACTURWG COMFANY, A CORPORATION OF PENNSYL- VANIA.

To all whom it may concern:

Be it known that I, SIDNEY W. Farms- WORTH, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Shielding Systems for Vapor-Converters, of which the following is a specification.

. My invention relates to shielding systems for vapor converters, and it has for its ob ject to provide means that shall minimize short circuiting and reverse arcing and otherwise improve the operation in apparatus of the character indicated.

In the accompanying drawing, Figure 1 is a side view, partially tially in section, of a vapor converter embodying two forms of my invention; and Fig. 2 is a side view, partially in elevation and partially in section, of a vapor converter embodying still another form ofmy invention.

In the operation of vapor converters and similar evacuated electric apparatus, current is, in general, conveyed between the electrodes by a stream of negative electrons emitted by the cathode and proceeding to the anode. The stream of electrons at the oathode may be excited by any of several well known methods, chief among which are. the

maintenance'of a keep-alive arc to the cath- I ode, the maintenance of the cathode at incandescence, the impact of a stream of positive ions thereagainst, and the impact of a beam of ultra-violet light.

If, in its passage from anode, an electron collides with a particle of residual gas, the particle is broken up into a positive ion and a negative electron, of which receive an initial impulse toward the anode by the impact. The newly freed negative electron moves on very rapidly because the propelling force of the electrostatic field is substantially coincidentin direction with the initial impulse thusgiven, but the newly freed positive ion moves but slowly and may soon come to rest and even reverse its direction of movement because of the neutralizing influence of the electrostatic field upon the initial impulse. Furthermore, the acceleration tending to be imparted; to the positive ion by the electrostatic field is much less than that of the because of the vastly larger negative electron although carrying, an

mass of the. former,

Specification. of Letters Patent.

in elevation and par-- vention, I show a vapor.

the cathode to an both SHIELDING- SYSTEM FOR VAPOBl-GONVERTEBS.

Patented July 3, 191 "2.

equal charge. The delivery of a glancing blow to a gas particle by an electron may disrupt the particle and force the resultant masses more or less transversely to the arc path into comparatively weak fields of electrostatic force. I

The passage of an anode'to a condition of negative polarity with respect to the cathode, such as happens periodically in a vapor converter, finds a large number of free positive ions afloat in and near the arc path without any well defined motion in any direction. These tramp ions are now-attracted to the temporarily negative anode and, if in sufficient number and sufficiently so energetically as to break down the negative electrode reluctance "thereof, causing short circuiting .or reverse arcing within the apparatus. This harmful action is especially liable to take place if thepositive ionsimpinge upon a globule of mercury or other foreign matter upon the electrode surface.

By my invention, ,I mount conducting members adjacent to electrodes subject: to the above described action and I charge said conducting members to such polarities that the said action is greatly reduced in intensity.

Referring to the accompanying drawing for a more detailed understanding of my inconverter at 3 in Fig. 1, provided with solid anodes i and 5 and with a cathode 6, preferably composed of vaporizable reconstructing material, such, for example, as mercury or suitable amalgams. JI-he two anodes 4: and 5 are connected; respectively, to the terminals of the secondary winding of a transformer 7, and the cathode 6 is connected to the mid point of said secondary winding through a load 8, as is customary in rectifier systems. The negative-electrode reluctance of the cathode 6 may be maintained ina broken-down condition by any suitable means, such, ample, as a keep-alive circuit 9, The anode 4 is surrounded by a metallic casing 10 profl vided with a transverse diaphragm 11 at its lower end. The diaphragm 11 is provided with a plurality of openings mounted short lengths of tubing 12-12 formed of conducting material. An insu- J lating member 13, mounted upon the member 10, carries a conducting platel iin which are mounted tubular members 15 similar to 110 accelerated, they may bombard the electrode for ex.- $00 wherein are the members 12 and preferably arranged in staggered relation thereto. The anode 4 is connected to the casing 10 through a resistance member 16 and, in like manner, the diaphragm 11 is connected to the plate 15 through a resistance member 17.

When the anode 4 is temporarily positive with respect to the cathode 6, a stream of negative electrons emitted from the latter passes through the tubular members 12 and possible production of a cathode spot, were it not for the fact that they are brought into intimate contact With the conducting shielding system, which is, at the same instant, also negative in polarity. The said positive ions are therefore collapsed upon the members 12 and 15, rather than upon the anode itself, and no destructive arc is produced thereby because of the choking effect of the resistance members 16 and 17.

When positive ions are being collapsed upon the tubular members 12 and 15, a small current is set up which results in potential drop in the resistance members 16 and 17. The fact that a greater total. resistance is included between the plate 14 and the anode than between the diaphragm 12 and the anode 4 results in a greater difference of potential and, consequently, the plate 14 is nearer in potential to the cathode 6 than is 4 the diaphragm 12.

. though operating in a more satisfactory It follows, therefore, that there are no extremely stee potential gradients within the container suc as would result in possible harmful efi'ects on the operation of the apparatus.

I show a shielding system associated-with the anode 5 in Fig. 1 which is essentially the same in theory and operation as that shown in connection with the anode 4, al-

manner because of differences in details of construction. A casing 10 surrounding the anode 5 is provided with a pair of transverse diaphragins 18 and 19 at the lower end thereof. The diaphra rality of conducting tu ular members 20-20 and the diaphragm 19 supports a pluralityof similar members 23-23. The tubes 20-20 are preferably arranged in staggered V relation to the tubes 2323 and all of said members are insulated by bushings 2121.

The tubular members 2323 are connect- 22, and the members 20.20 are connected with respect to each other.

18 supports a plu relation to a cathode 6. An anode shield 24 is provided with two transverse insulating dlaphragms 25 and 26 which, in turn, sup

port conducting tubular members 27 'and 28, preferably mounted in staggered relation The tubular members 28 are connected to the anode 23 through a resistance member 29, and the tubular members 2727 are connected to an intermediate point in the resistance memb'er.29, so that the two setsof tubular members are maintained at slightly difl'erent po tentials, in a manner similar to that shown in connection with the anode 5 in Fig. l.

If it be desired to obtain an even more complete neutralization of the positive space charge and a more gradual potential gradient, the anode may be protected by more than two groups of collapsing tubes, and various other expedients may be resorted to for ob aining a more inimate contact between t e arc and the collapsing apparatus.

I am aware of U. S. Patent #1,110,600,

issued to Percy H. Thomas on Sept. 15,-

gradients are avoided. This last named feature in my device amounts to more than mere duplication of the Thomas shield because, at voltages higher than a certain minimum, it is difficult to obtain satisfactory operationwith a single shield, whereas, by multiplying the number of shields in accordance with the operating voltage and b potenti l. therethrough, satisfactory,;opera tion may be secured at any desired voltage.

Furthermore, in the apparatus of Thomas, it is necessary to employ a throat member maintaining an even gradation of of comparatively large cross section in orderthat an undue constriction be not imposed upon the power arc, such as would result in a radical increase of the resistance of the arc path. A throat member sufliciently large to comply with this condition, in a commercial converter, would be so large that many positive tramp ions would be able to pass therethrough, even in spite of the electrostatic charge on said throat memher. With the construction which I have disclosed, however, thearc is forced to traverse a large number of throat members, each of comparatively small cross sectional area.

By providing a 'sufiiciently large number of 1:0

such throat members, 'no constricting influence is imposed upon the are but, nevertheless, all portions of the are are caused to pass extremely close to an electrostatirally charged wall. The main free path of the positive tramp ions between successive impacts is fairly large and said ions therefore describe a zig-zag course as they move toward the temporarily negative anode. Said zig-zag course appears to lead, in substantially all cases, into such operative proximity to the wall of a throat member that the electrostatic attraction of said wall overcomes the inertia of the positive tramp ion, collapsing the same and preventing its passage to the anode.

Throughout this description, I have explained the action of my device in accordance with the theory -which seems most plausible in view of the present knowledge of the underlying phenomena. I desire it to be distinctly understood, however, that I do not confine myself to said theory of operation but merely present the same to aid in an understanding of the invention.

While I have shown my invention in its preferred form, it will be obvious to those skilled in the art that it is susceptible of various minor changes and modifications without departing from the spirit thereof, and I desire, therefore, that no limitations shall be placed thereupon except such as are imposed by the prior art or are specifically set forth in the appended claims.

I claim as my invention:

1. In a vacuum-type converter, the combination with an electrode, of a shielding member surrounding said electrode and provided with a tubular, conducting, arc-admitting member, and a conducting connection from said tubular member to a source of potential of like polarity to said electrode, the diameter of the arc-admitting opening being so small as to cause substantially all the positive tramp ions to come within the electrostatic influence of the walls thereof.

2. In a vacuum-type converter, the 06inbination with an electrode, of a shielding member surrounding said electrode and provided with a tubular, conducting, arc-ad- 'mitting member,

' tion from said tubular member to ,said electrode, the diameter of the arc-admitting opening being so of being so great that substantially all the positive tramp ions come within theelectrostatie influence of the walls thereof in attempting to traverse said opening.

, 3. In a vacuum-type converter, the combination-with an electrode, of a shielding member surrounding said electrode and provided with a tubular, conducting, arc-admitting member, a conductmg connection from said tubular member to said electrode,

the arc-admitting opening and a conducting connec-' small and the length thereand a current-limiting device in said connection,v the diameter'of the arc-admitting opening bein so small and the length i said opening ing so great that one of the mean free paths of substantially every positive tramp ion attempting to traverse said opening leads into such proximity to a wall of said opening as to cause said ion to be held by said Wall.

4. In a vacuum-type converter, the combination with an anode which is periodically negative in polarity, of a shieldin member surrounding said anode and provided with a tubular, conducting, arc-admitting member, and a conducting connection from said tubular member to a source of potential of the diameter of like polarity to said anode,

being so small as to cause substantially all the positive tramp ions to come within the electrostatic infiuence of the Walls thereof.

5. In a vacuum-type converter, the combination with an anode which is periodically negative in polarity, of a shielding member surrounding said anode and provided with a tubular, conducting, arc-admitting member, and a conducting connection from said tubular member to said anode, the diameter of the arc-admitting opening being so small and the length thereof being so great that substantially all the positive tramp ions come within the electrostatic influence of the walls thereof in attempting to traverse said opening.

'6. In a vacuum-type converter, the combination with an anode which is periodically negative in polarity, of a shieldin member surrounding said anode and provided with a tubular, conducting, arc-admitting member, a conducting connection from said tubular member to said anode, and a currentlimiting device in said connection, the diameter of the arc-admitting opening being so small and the length of said opening being so eat that one of the mean free paths of substantially every positive tramp ion attempting to traverse said openin into such proximity to a wall of said leads openwall.

7. In avacuum-typeconverter, the combination with an anode, of a shielding member surrounding said anode and provided with. an insulated, tubular, conducting, arcadmitting member, and a connection from said tubular member to a source of potential varying in synchronism with the potential of said anode, the diameter of the arc-admitting opening being so small as to cause substantially all the positive tramp ions to come within the eleetnost the walls thereof.

8. In a vacuum-type converter, the combination with an anode, of a shielding member surrounding said anode, and provided tic influence of Witha plurality of insulated, tubular, conducting, arc-admitting members arranged so that the arc passes through themin succession, and connections from said tubular members to said anode, the tubular openings in each of said members bein so small and of such length that substantially all posi- .tive tramp ions, in attempting to pass therethrough, 'come within the electrostatic influence of the walls thereof.

9. In a vacuum-type converter, the combination with an anode,'of a shielding member surrounding said anode and provided with a plurality of insulated tubular conducting arc-admitting members so arranged that the arc passes through them in succe'ssion, a connection from said anode to each of said tubular members, a resistance member inserted in one of said connections,

2 and a resistance member of diflerent value inserted in the other connection.

, 10. In a vacuum-type converter, thecombination with an anode, of a shielding member surrounding said anode and provided with a plurality of insulated tubular conducting arc-admitting members arranged so that the arc passes through them in succes- 'sion, a connection from said anode to each of said tubular members, a resistance member inserted in the connection to the tubular member nearest to the anode, and a resistance member of greater value inserted in including current-limiting devices from said anode to said groups of tubular members.

12. In a vacuum-type convertenthe combination with an anode, .of a shielding member surrounding said anode and provided with a group of tubular conducting arc-ad 1 mitting members, a second group of similar arc-admitting members disposed at a difl'erent point in the arc stream, connections including a resistance member from said anode to the group disposed nearer thereto'in the arc stream, and a connection including a resistance member of greater value between 55 said anode and the remaining group.

13. In a vacuum-type converter, the combination with a pair of electrodes, of means for initiating and maintaining an are therebetween,- a plurality..of perforated conducting members mounted between said electrodes so that said arc asses therethrough in succession, and con ucting connections between said conducting members and one of said electrodes, the openings in each of said members being so small and of suchlength thereof.

that substantially all positive tramp. ions, I

in attempting to pass therethrough, come within the electrostatic influence of the walls thereof. 14. In a vacuum-.type-converter, the combination withv a pair of electrodes, of means for initiating and maintaining an are therebetween, a plurality of perforated conducting members mounted between said electrodes so that said arc passes therethrough in succession, and conducting connections, including resistance members, between said conducting members and "one of said electrodes, the openin in each of said members being so small an of such length that substantially all positive tramp ions, in attempting to pa$ therethrough, come within theelectrostatic influence of the walls thereof. 1

15. In a vacuum-type converter, the combination with a pair of electrodes, of means for initiating and maintaining an are therebetween, a plurality of groups of tubular conducting members mounted between said electrodesl sothat said are passes therethrough in succession, and conductin connections including resistors between sald conducting members and one of said-electrodes, the connectionto the group nearest said electrode in the arc path having a minimum resistance and the groups mounted at greater distances having correspondingly greater resistances in the connections thereto.

16. In a vacuum-type converter, the combination with an anode which is periodically negative in polarity, of a shielding member therefor provided with a plurality of perforations, a tubular, conducting, lining member mounted in each of said perforations, and means tending to impart a negative charge to said lining members at all times when said anode is negative in polarity, the

joint cross-section of the openings through said lining members being sufiiciently large to produce substantially no diminution m the cross-section of a power-arc operating to said anode, and the crosssection of the opening through each lining member being 1 so small and the length thereof so great that substantially all positive tramp ions .attempting to pass therethrough comewithin the electrostatic influence of the walls 17 In a vacuum-type converter, the com-. bination with an anode whichis periodically 2 negativeiupolarity, of a shielding member therefor provided with a laminated wall portion, the laminations of said wall or tion being spaced apart and being provided with perforations, a tubular, conducting lining member mounted ineach ofsaid perforav tions, and means tendin toimpart a negative charge to said linmg members atv all I times when said anode is negative in polar- 1ty,'the oint cross-section of the openings 130 through said lining members being Suficiently large to produce substantially no diminution in the cross-section of a poWer-.

arcoperating to said anode, and the crosssection of the opening through each lining member being so small and the length thereof so great that substantially all positive tramp ions attempting to pass therethrough come within the electrostatic influence of the Walls thereof.

18. In a vacuum-type converter, the combination with an anode which is periodically negative in polarity, of a shielding member therefor provided with a laminated Wall portion, the laminations of said wall portion bein spaced apart and being provided with per orations, a tubular, conducting lining member mounted in each of said perforations, means tending to impart a negative charge to the lining members mounted in the wall lamination nearest the anode at all times When said anode is negative in potential, means tending to impart successively smaller and smaller negative charges to the lining members mounted in the laminations at successsively greater distances from said anode when said anode is negative in polarity, the joint cross-section of the openings through said lining members being sufficiently large to produce. substantially no diminution in the cross-section of a ,powerare operatingto said anode, and the crosssection of the opening through each lining member being so small and the length thereof so great that substantially all positive tramp ions attempting to pass therethrough come Within the electrostatic influence of the Walls thereof.

In testimony whereof, I have hereunto subscribed my name this 30th day of July SIDNEY W. FARNSWORTH. 

